Well I suppose you could have a look at how literature can be responsible for leisure activities like the theater, plays, poetry readings, literature societies, movies etc. These all allow people to come together. So what i am trying to say is that maybe you should look at how the production of literature allows groups of people to come together and socialize. Hope that helps.
Literature does have a social value. Social structures are created through interaction and commonality. Any shared literature, any media to be exact, that touches peoples lives in a society will have social influence on the people therefore it will have social value.
In addition to a la carte, literature is very influential in shaping the minds of the people who read them. It can bring hope to a dystopian society or bring down a Utopian culture with thoughts of licentiousness.
It is in fact the very medium of societal development. Apart from TV's and net now; but for an intro, you could try elaborating on how literature played a major role in socities in the past and how it is right now, in the present.